This proposal is an experimental plan to evaluate the therapeutic effectiveness of boron neutron capture therapy (BNCT) for the treatment of brain tumors. Brain tumor bearing neonate beagles will be treated by BNCT with a range of radiation doses delivered in a single acute irradiation. Treated animals will be sacrificed at different time periods (7, 14, 21, 45 days) post-irradiation to assess the evolvement of tumoricidal effect produced. Normal animals (neonate beagles and young monkeys) will be neutron irradiated after 10B compound infusion to observe late occurring radiation effects, especially within intracranial tissues at risk. Clinical observation of these growing animals before sacrifice will aid in the full assessment of the radiation effects, in vivo. 10B enriched Na2B12H11SH manufactured by a U.S. company, will be the boron compound used for all these studies. Neutron induced alpha-autoradiography will be developed to measure the microscopic distribution of 10B within cells of tumor, brain and other tissues and thereby allow an accurate determination of 10B dose at the cellular level. The increase of the neutron flux distribution in tissue will be investigated by changing the therapy beam of the MITR-II, and the concomitant biological effects will be measured using the same animal model.